1. Field of the Invention
This invention pertains to the field of valves and valve actuators. More particularly, this invention pertains to a valve for positioning between a source of fluid, such as an above-ground fuel tank, and a transfer pump, used to pump the fluid to a destination, such as to a vehicle fuel tank, the valve operating to open when the pump is turned on and to close when the pump is turned off to prevent a continuation of flow due to siphoning.
2. Description of the Prior Art
In delivering liquids, such as fuels, from underground tanks to an above-ground destination, the transfer pump starts with a negative head and must draw the liquid upward before pumping it to the destination, such as into an automobile fuel tank. When the transfer pump is shut off, the flow of fuel in the transfer line immediately ceases due to the gravitational pull on the liquid. Recent environmental protection legislation calls for the fuel to be stored in above-ground tanks. This has shifted the static hydraulic situation from a negative head to a positive static head against the transfer pump. Gravity actually aids in this situation in the transfer of liquid by providing a positive pressure on the intake side of the transfer pump. A danger exists, however, in that the fuel will continue to flow by siphon action after the pump is turned off. This will cause the fuel to flow through the pump even after the pump is motionless thereby creating a fire or explosion hazard. Older pumps that draw fuel from underground tanks cannot be used to pump fuel from above-ground tanks without extensive reworking.
An electric shut-off valve could be used to open and close the transfer line when power is applied and then cut off to the pump. This is expensive, however, because of all the safe guards required to prevent the electricity from causing a fire or explosion in the fuel that has leaked from the pump. Accordingly, the prior art has not been able to develop a mechanically-operated valve having sufficient reliability to inhibit siphon flow that satisfies the demands of the fuel industry.